A vehicle with an actuator driven clutch to control the engagement of the engine and the transmission has already been put to practical use. In such a vehicle it is possible to automatically make a series of transmission operations such as clutch disengagement, gear shifts, and clutch reengagement based on a transmission command input by a rider.
When a vehicle with an engine starts traveling from a stand still state, accelerator operation by a rider and a rotational speed of the engine are detected, a clutch position is changed according to a result of the detection, and the clutch is shifted from the disengaged state to the engaged state. For example, Japanese Utility Application JP-A-2006-170229 discloses that starting control is initiated when the accelerator opening becomes larger than a prescribed opening and the clutch is moved and engaged as the engine speed increases.
Focusing on the state of the clutch, the starting control disclosed in Japanese Utility Application JP-A-2006-170229 is controlled to make a shift from a state where the clutch is disengaged to a state where the clutch is engaged. A clutch change in state from disengaged to engaged is typically used in starting the vehicle. However, such control is required not only in starting but also in other situations.
For example, there is a case when a vehicle may be coasting without the clutch being engaged and the operator wants to engage the clutch to travel under the power of the engine. This requires the clutch to make a shift from a disengaged state to an engaged state while the vehicle is moving at a certain speed. Such a situation does not frequently occur. However, engaging the clutch while the vehicle is in motion may occur, for example, when a vehicle stops or decelerates on a downhill. In addition, a situation may occur while traveling with the clutch disengaged and the engine stops running for some reason, such as turning off of a main key, and thereafter the main key is turned on again while still traveling under the force of momentum.
When a vehicle is traveling under its own momentum and the clutch is thereafter engaged, the rotational speed on the downstream side of the clutch, i.e., the rotational speed on the side of the driving wheel, can be higher than the rotational speed on the upstream side of the clutch, i.e., the rotational speed on the side of the engine. In this case, if the starting control disclosed in Japanese Utility Application JP-A-2006-170229 is used, the rotational speed on the downstream side of the clutch and, further, the rotational speed of the driving wheel may be abruptly decreased when the clutch is engaged. The abrupt decrease is caused because the rotational speed on the downstream side of the clutch is not taken into consideration by the starting control before engaging the clutch. This may result in an undesirably large braking force being applied to the vehicle, causing the riding comfort of the rider to deteriorate.
The present invention is made in consideration of such a problem and an object is to control the engagement of an actuator driven clutch from a disengaged state to an engaged state while the vehicle is traveling, without sacrificing riding comfort.